The use of molecular sieves with a variety of binders is well known to the art. With the develoment of new and/or improved applications for molecular sieves requiring the use of various molecular sieves having increasingly higher SiO.sub.2 /Al.sub.2 O.sub.3 ratios and a concurrent desire to bind such sieves with a silica binder, the problem of obtaining a satisfactory bond between the sieve and the silica bonding agent, has received increasing attention.
As the SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a molecular sieve increases the bonding of these materials become more difficult particularly when silica is used as a binder. The increase in negative surface charge is associated with the increase in silica present on the sieve surface which cuses repulsion between the sieve and the binder thus resulting in poor strength. Up to the present time, alkali metal ions have been used a cross-linking agents in the silica bonding of silica rich molecular sieves, however, this route is prohibitive for some catalyst applications, since such agents adversely effect the activity and/or performance of the resultant catalyst.
The following represents an overview of some of the more recent attempts to address the problem, and reflects the current state of the art in this area:
European Application EP-167324-Bowes), filed Jan. 8, 1986, discloses SiO.sub.2 -rich extrudates which are prepared by mixing a siliceous solid (for example SiO.sub.2 and a zeolite) with water and a alkali metal compound to give a mixture with a total solids content of 25-75 wt. % and an alkali metal content of 0.25-10 wt. % calculated on a dry basis.
German Often. De 1944879 (WACKS) Mar. 11, 1971 teaches silica-bonded molecular sieves of unreduced apparent pore diameter which are prepared by mixing zeolites with (NaPO.sub.3).sub.3 and K silicate, drying and removing at K.sub.2 HPO.sub.4.
U.S. Pat. No. 3,867,279 (Young), which issued Feb. 18, 1975, discloses a catalytic cracking process which employs SiO.sub.2 onded silicate particles having improved crush strength which are prepared by mixing reactive SiO.sub.2 sols with the siliceous particles in an aqueous medium under conditions of temperature and contact time sufficient to at least partially bond the sol and silicate.
Japanese Pat. No. JP 49/203638 (Asahi Glass Co.), Nov. 17, 1984, teaches a mixture of SiO.sub.2 gel and zeolite which is pelletized to form a desiccant for automobile air conditioner refrigerant.
Japanese Pat. No. JP 60/68536 Sept. 2, 1985 teaches granular adsorbents bound by synthetic resin binders having continuous pores. These materials are mixed, press-molded to a degree that the grains are in contact with each other and then dried to yield adsorbent moldings.
None of the aforementioned prior art references disclose the method of the present invention nor the advantages to be achieved by carrying out the steps herein disclosed by the applicants.